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Re: [atm_free] Re: [interferometry] Improved igrams for 1-meter mirror, progress on the surface

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  • George Loyer
    The lens is a Canon 50mm f1.4. The clips are what now look like gigantic pieces of tape to help us be clear on the orientation and to assure us that we are
    Message 1 of 7 , Feb 2, 2013
      The lens is a Canon 50mm  f1.4.  The "clips" are what now look like gigantic pieces of tape to help us be clear on the orientation and to assure us that we are not getting a reversed image. We've been talking about taking an image in each orientation with a movable pointer obstruction and removing it for the igrams that will be used for analysis.  I'm interested in the PSI but we are all daunted by the vibration issues described on the list. You would all laugh if you saw us making an igram for this beast - the mirror is one corner of the the garage/shop, and the interferometer is through the kitchen door and sitting on the kitchen floor. :-)
      George


      On Thu, Jan 31, 2013 at 11:28 PM, Vladimir <elizabeta.galogaza1@...> wrote:
       

      Georg,
       
      Which camera lens are you using now?
      The interferograms are exceptional . Perfect edge, very good contrast,
      And progress is evident in reports.
       
      For kind of mirrors you are after (big and fast), upgrading  to PSI will be sure bet.
      No more problems with closed fringes and lot of tilt to have them open.
      The quality of your setup will warant the success with miniscule investment
      in additional components. It will by no means go into way of your figuring
      robotics because available data are same as in OF. Additional benefit will
      be posibility of the  easy tayloring of analysis software output to your specific needs.
      In any case something  to think about in future.
       
      Can you made clips less disturbing for the interferogram edge?
       
      Thanks for posting on this intersting project.
       
      Vladimir.
       
      Do the clips have to be so visible on the mirror edge, disrupting somehow
      the interferogram?
       
       
      ----- Original Message -----
      Sent: Friday, February 01, 2013 12:23 AM
      Subject: [interferometry] Improved igrams for 1-meter mirror, progress on the surface [1 Attachment]

       

      Vladimir made no bones about our fancy interferometer and the reason for our difficulty in getting a complete igram all of a sudden - the distance from the diverging lens to the beam splitter was over 25mm and that meant that the diverging reference beam, back from the mirror, was diverging too "soon" for the aperture of the camera lens we were using. 

      We remedied two things - we used the right camera lens and we mounted the diverging lens on a two-bit piece of aluminum to get it within a few mm of the beam splitter. The combo got us what we needed, and we have good igrams again for analyzing.


      You were right, Vladimir!


      Now we are working on the surface with a sub-diameter tool (660mm) and you can see the difference in these two OF reports the progress we are beginning to make.  Thanks for your help, and we'll keep the group posted. Glad for any additional thoughts as you look at our data and our igrams.

      George

      --
      George Loyer
      707.548.2110 cell

      No virus found in this message.
      Checked by AVG - www.avg.com
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      --
      George Loyer
      707.548.2110 cell
    • Vladimir
      Georg, I think nobody will laugh looking at 1m mirror. I wonder if you have more problems with vibrations or turbulence. With 7m distance to the mirror both
      Message 2 of 7 , Feb 2, 2013
        Georg,
         
        I think nobody will laugh looking at 1m mirror.
        I wonder if you have more problems with vibrations or turbulence.
        With 7m distance to the mirror both must be great pain. 
         
        Vladimir.
         
        ----- Original Message -----
        Sent: Saturday, February 02, 2013 2:14 PM
        Subject: Re: [atm_free] Re: [interferometry] Improved igrams for 1-meter mirror, progress on the surface

         

        The lens is a Canon 50mm  f1.4.  The "clips" are what now look like gigantic pieces of tape to help us be clear on the orientation and to assure us that we are not getting a reversed image. We've been talking about taking an image in each orientation with a movable pointer obstruction and removing it for the igrams that will be used for analysis.  I'm interested in the PSI but we are all daunted by the vibration issues described on the list. You would all laugh if you saw us making an igram for this beast - the mirror is one corner of the the garage/shop, and the interferometer is through the kitchen door and sitting on the kitchen floor. :-)
        George


        On Thu, Jan 31, 2013 at 11:28 PM, Vladimir <elizabeta.galogaza1@...> wrote:
         

        Georg,
         
        Which camera lens are you using now?
        The interferograms are exceptional . Perfect edge, very good contrast,
        And progress is evident in reports.
         
        For kind of mirrors you are after (big and fast), upgrading  to PSI will be sure bet.
        No more problems with closed fringes and lot of tilt to have them open.
        The quality of your setup will warant the success with miniscule investment
        in additional components. It will by no means go into way of your figuring
        robotics because available data are same as in OF. Additional benefit will
        be posibility of the  easy tayloring of analysis software output to your specific needs.
        In any case something  to think about in future.
         
        Can you made clips less disturbing for the interferogram edge?
         
        Thanks for posting on this intersting project.
         
        Vladimir.
         
        Do the clips have to be so visible on the mirror edge, disrupting somehow
        the interferogram?
         
         
        ----- Original Message -----
        Sent: Friday, February 01, 2013 12:23 AM
        Subject: [interferometry] Improved igrams for 1-meter mirror, progress on the surface [1 Attachment]

         

        Vladimir made no bones about our fancy interferometer and the reason for our difficulty in getting a complete igram all of a sudden - the distance from the diverging lens to the beam splitter was over 25mm and that meant that the diverging reference beam, back from the mirror, was diverging too "soon" for the aperture of the camera lens we were using. 

        We remedied two things - we used the right camera lens and we mounted the diverging lens on a two-bit piece of aluminum to get it within a few mm of the beam splitter. The combo got us what we needed, and we have good igrams again for analyzing.


        You were right, Vladimir!


        Now we are working on the surface with a sub-diameter tool (660mm) and you can see the difference in these two OF reports the progress we are beginning to make.  Thanks for your help, and we'll keep the group posted. Glad for any additional thoughts as you look at our data and our igrams.

        George

        --
        George Loyer
        707.548.2110 cell

        No virus found in this message.
        Checked by AVG - www.avg.com
        Version: 2013.0.2890 / Virus Database: 2639/6072 - Release Date: 01/31/13




        --
        George Loyer
        707.548.2110 cell

        No virus found in this message.
        Checked by AVG - www.avg.com
        Version: 2013.0.2897 / Virus Database: 2639/6074 - Release Date: 02/01/13

      • George Loyer
        Vladimir, We get the camera in position, then stand very still for a few seconds and then snap the picture. Getting the igram can be a problem, but we
        Message 3 of 7 , Feb 2, 2013
          Vladimir,
          We get the camera in position, then stand very still for a few seconds and then snap the picture. Getting the igram can be a problem, but we eventually figured out how to not move our bodies while we're adjusting the xyz platform and that seems to work well enough.
          George

          Sent from my iPad

          On Feb 2, 2013, at 5:44 AM, Vladimir <elizabeta.galogaza1@...> wrote:

           

          Georg,
           
          I think nobody will laugh looking at 1m mirror.
          I wonder if you have more problems with vibrations or turbulence.
          With 7m distance to the mirror both must be great pain. 
           
          Vladimir.
           
          ----- Original Message -----
          Sent: Saturday, February 02, 2013 2:14 PM
          Subject: Re: [atm_free] Re: [interferometry] Improved igrams for 1-meter mirror, progress on the surface

           

          The lens is a Canon 50mm  f1.4.  The "clips" are what now look like gigantic pieces of tape to help us be clear on the orientation and to assure us that we are not getting a reversed image. We've been talking about taking an image in each orientation with a movable pointer obstruction and removing it for the igrams that will be used for analysis.  I'm interested in the PSI but we are all daunted by the vibration issues described on the list. You would all laugh if you saw us making an igram for this beast - the mirror is one corner of the the garage/shop, and the interferometer is through the kitchen door and sitting on the kitchen floor. :-)
          George


          On Thu, Jan 31, 2013 at 11:28 PM, Vladimir <elizabeta.galogaza1@...> wrote:
           

          Georg,
           
          Which camera lens are you using now?
          The interferograms are exceptional . Perfect edge, very good contrast,
          And progress is evident in reports.
           
          For kind of mirrors you are after (big and fast), upgrading  to PSI will be sure bet.
          No more problems with closed fringes and lot of tilt to have them open.
          The quality of your setup will warant the success with miniscule investment
          in additional components. It will by no means go into way of your figuring
          robotics because available data are same as in OF. Additional benefit will
          be posibility of the  easy tayloring of analysis software output to your specific needs.
          In any case something  to think about in future.
           
          Can you made clips less disturbing for the interferogram edge?
           
          Thanks for posting on this intersting project.
           
          Vladimir.
           
          Do the clips have to be so visible on the mirror edge, disrupting somehow
          the interferogram?
           
           
          ----- Original Message -----
          Sent: Friday, February 01, 2013 12:23 AM
          Subject: [interferometry] Improved igrams for 1-meter mirror, progress on the surface [1 Attachment]

           

          Vladimir made no bones about our fancy interferometer and the reason for our difficulty in getting a complete igram all of a sudden - the distance from the diverging lens to the beam splitter was over 25mm and that meant that the diverging reference beam, back from the mirror, was diverging too "soon" for the aperture of the camera lens we were using. 

          We remedied two things - we used the right camera lens and we mounted the diverging lens on a two-bit piece of aluminum to get it within a few mm of the beam splitter. The combo got us what we needed, and we have good igrams again for analyzing.


          You were right, Vladimir!


          Now we are working on the surface with a sub-diameter tool (660mm) and you can see the difference in these two OF reports the progress we are beginning to make.  Thanks for your help, and we'll keep the group posted. Glad for any additional thoughts as you look at our data and our igrams.

          George

          --
          George Loyer
          707.548.2110 cell

          No virus found in this message.
          Checked by AVG - www.avg.com
          Version: 2013.0.2890 / Virus Database: 2639/6072 - Release Date: 01/31/13




          --
          George Loyer
          707.548.2110 cell

          No virus found in this message.
          Checked by AVG - www.avg.com
          Version: 2013.0.2897 / Virus Database: 2639/6074 - Release Date: 02/01/13

        • paul valleli
          All, The use of clips is quite critical for robotic polishing tasks and for local hand rubbng. When working small areas it can be a disaster if one rubs in a
          Message 4 of 7 , Feb 2, 2013
            All,
            The use of clips is quite critical for robotic polishing tasks and for
            local hand rubbng.
            When working small areas it can be a disaster if one rubs in a low
            area of the mirror surface.
            We call them "fiducials" and are actually engraved into the surface so
            that the references can never be lost.
            Sometimes it is almost impossible to get rid of dust motes that smear
            a usable interferogram with dark diffraction blotches. We simply
            import the I/F into photoshop and paint out the offending area.
            Also, most analysis programs cannot effectively handle the case of a
            perforated mirror without giving spurious or simply wrong test
            results. In that case, we paint in imaginary fringes across the
            center, being careful not to lose the fringe order.
            We then ignore the results in that area of the surface error map.
            One must be brutally honest to not fudge the data as nothing is to be
            gained if a rogue mirror is put into service, only to find it doesn't
            work.
            The Smartt PSI ( I assume this is what is being referred to) is a
            single pass tester which has the advantage of minimizing air currents
            but the point source usually has to be generated by a collimating
            system of like aperture. If one has superb seeing conditions, free of
            air currents, then a star can be the source. If the star is not at the
            poles, it must be carefully tracked in a working mount.
            The PSI can be used in the autocollimation test method if the source
            and I/F are allowed to be slightly offset from each other.
            I actually made 16mm films of a 1 Meter F/8 Paraboloid in 1963. It was
            tested at the center of curvature with a proto-type unequal path
            interferometer. The design was later attributed to Roland Shack in
            Arizona. The vibration was terrible over the 16 Meter optical path
            despite the building foundation being built over a sand pit.

            Starman Paul
          • atmpob
            Paul, The PSI being referred to is Phase Shift Interferometry. Additional polarizers and 1/4 wave plate can be added to the Bath interferometer that shift the
            Message 5 of 7 , Feb 2, 2013
              Paul,
              The PSI being referred to is Phase Shift Interferometry. Additional polarizers and 1/4 wave plate can be added to the Bath interferometer that shift the phase of the interferogram. Special analysis software can then deduce the surface from several shifts in the phase. It is a more advanced technique than the FFT analysis technique used in OpenFringe. It's advantage over the FFT method is that it does not require a large amount of tilt to the wavefront that create a lot of fringes. It can be a benifit when testing large fast mirrors at ROC. The disadvantage is it makes the Bath a little more complicated but still within the realm of the average ATMer.

              Dale Eason

              --- In atm_free@yahoogroups.com, paul valleli wrote:
              >....snip
              > The Smartt PSI ( I assume this is what is being referred to) is a
              > single pass tester which has the advantage of minimizing air currents...
            • paul valleli
              Oh!, of course, Dale ! I was visiting John Buccini when he was working on a PS system for the MIC-1 LUPI many years ago. Also our Zygo s were phase shifters.
              Message 6 of 7 , Feb 3, 2013
                Oh!, of course, Dale !
                I was visiting John Buccini when he was working on a PS system
                for the MIC-1 LUPI many years ago. Also our Zygo's
                were phase shifters.
                Sometimes, this world uses too many acronyms
                and it also shows how old I am.
                Ray Smartt's interferometer was a PDI - Point Diffraction Interferometer
                and had the important advantage of a single pass test so a star
                could be used as a full-up system test. It also incorporated
                a wave plate but we did not succeed in making our own working
                instrument. Ray did not consider it a worthwhile business, either.
                Paul
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